Yet the performance of skipper Nemanja Vidic was equally notable, as he guided United to only their fourth Premier League clean sheet of the season after Gareth McAuley's early own goal had put the hosts in front against West Brom.

Plagued by injury for the past 16 months, and restored to the United line-up for the only the second time since his most recent knee operation, Serbian Vidic used all of his experience to ensure the hosts were not made to pay for a lacklustre second-half display.

And when Van Persie curled home a brilliant effort in the final minute, the Red Devils` handsome seven-point lead at the top of the table was preserved.

After all the furore around Ferguson's confrontation with Mike Dean on Boxing Day, mascot Fred the Red probably approached the United boss with a degree of trepidation as the pair met on the touchline prior to kick off.

The exchange was cordial, though, as was the jocular encounter between Ferguson and fourth official Phil Dowd shortly afterwards.

And once the match started, referee Jon Moss did little to get the United manager vexed, beyond an inexplicable free-kick against Tom Cleverley when the midfielder had been looking at a dropping ball on the edge of his own box when Billy Jones crashed into him.

By that point, United had got their noses in front courtesy of McAuley, who could only divert a bullet cross from Ashley Young into his own net.

The nearest United went to doubling their lead was when Young strode onto a deflected Antonio Valencia cross.

He hit it sweetly on the half volley, only for former Red Devils keeper Ben Foster to respond with a brilliant save, which earned his slice of good fortune when he shoved the ball onto the crossbar and over.

Danny Welbeck - afforded a rare start in a central striking berth - and Shinji Kagawa - back for the first time since suffering a knee injury in October - both sparkled for the hosts, who were so obviously on top.

With a defence that has leaked so many goals this season, Ferguson would not have felt safe.

Yet the presence of Vidic offered some degree of comfort.

The Serbian has been absent so often over the past 15 months it has almost been forgotten what a calming influence he is.

His bravery is unquestioned too. And when Chris Brunt drilled a free-kick goalwards in the final throes of the opening period, it was no surprise Vidic should be the one to emerge from a crowd of bodies having headed it away.

However, with the clock ticking by and heavy rain continuing to pour down on a sodden surface that required a precautionary inspection a couple of hours before kick-off, United started to get stuck.

Young completely miskicked when Valencia's cross presented a golden opportunity on the hour, which offered a Baggies outfit already growing in self-belief more reason for optimism.

Had Brunt's piledriver been either side of David de Gea it surely would have brought the visitors level.

As it was, the shot went straight to the Spain keeper.

Little wonder Van Persie's arrival midway through the second period was greeted with such enthusiasm, underlining the Dutchman's influence since his summer move from Arsenal.

West Brom were in the mood, though.

And with United's passing becoming increasingly sloppy, they continued to push on with force.

Vidic needed to be in the right place to clear a Romelu Lukaku cross that threatened panic inside the United six-yard box and the sight of his fellow defenders throwing themselves at anything that moved, it had turned into an unedifying backs-to-the-wall effort so unlike the thrill-a-minute action this stadium has become used to.

Van Persie was denied by Foster with nine minutes remaining but the former England keeper could do nothing about the Dutchman's late shot, which curled expertly into the top corner from Paul Scholes' pass.